@article{10_4064_fm214_2_1,
     author = {Tomonori Fukunaga},
     title = {Homotopy classification of nanophrases 
 with at most four letters},
     journal = {Fundamenta Mathematicae},
     pages = {101--118},
     publisher = {mathdoc},
     volume = {214},
     number = {2},
     year = {2011},
     doi = {10.4064/fm214-2-1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/fm214-2-1/}
}